Sound-translating device



March 20, 1934. A. S. RINGEL SOUND TRANSLATI NG DEVI CE Filed Feb. 12,1951 A TTORNEY.

Patented Mar. 2i), 1934 SOUND-TRANSLTING DEVICE Abraham Somer Ringel,lVlerchantville,- N. J., as'- slgnor, by mesne assignments, to RadioCorporation of America, New York, N, Y., a corporation of DelawareApplication February v12, 1931, Serial No. 515,190

17 Claims.

My invention relates to sound-translating devices, such as loudspeakersand microphones, and it has particular relation to translating devicesof the electrodynamic type.

In all sound-translating devices of the electrodynamic or moving coiltype, with which I am familiar, the magnetic system extends away fromthe cone and coil, thereby occupying considerable space. Such devices,particularly loudspeakers 1c intended for use in midget radio receivers,take up space that can be used to advantage for other radio apparatus.Furthermore, in centralized radio installations of the type wherein eachloudspeaker is disposed in a small niche in the Wall iii of a room, itis highly important that the frontto-back dimension of the apparatus beas small as possible, and that the moving parts thereof be protectedagainst damage.

It is, accordingly, an object of my invention to zo provide asound-translating device that shall occupy minimum space compatible withefficiency.

Another object of my invention is to provide a sound-translating devicewherein all moving parts are adequately protected against damage.

Another object of my invention is to provide a sound-translating devicethat may be mounted as a unit in a shallow depression in the wall of aroom.

Another object of my invention is to provide a loudspeaker that shall besubstantially non-directive.

An additional object of my invention is to provide improved means forsupplying a loudspeaker with currents at audio frequencies.

A still further and more specic object of my invention is to provide, ina device of the type described, centering means for the moving coil thatshall be easily accessible for adjustment.

The foregoing objects and others related thereto I accomplish, in part,by disposing certain of the magnetic system elements of asound-translating device exteriorly of a substantially conicaldiaphragm, or a diaphragm having any other desired shape, and bydisposing the remainder of the magnetic system elements substantiallyentirely within the space bounded by the diaphragm. I, furthermore,utilize one of the said magnetic system elements as a support for thelarge end of the diaphragm and provide the said element with a pluralityof openings whereby it serves as an ornamental and protective grille andas an acoustic lter.

In a preferred embodiment of my invention hereinafter described, theremainder of the magnetic system elements, which are entirely within thespace bounded by the diaphragm, includes' an element of the magneticsystem such as a central pole piece arranged Vto extend entirely throughsuch space.

It` should be understood that the space bounded by the inner surface ofsaid diaphragm includes such space as may be considered to be includedwithin the diaphragmvwhen the latter is regarded as a containeri orenclosing element per se. Regarding a conical diaphragm in the manner inwhich it is usually employed, with the base or periphery portionextending frontally,v such space is that located within the confines ofthe conical diaphragm on the front face thereof. More briey and moregenerally stated, the space bounded by the inner surface of thediaphragm may be regarded as the space within the conical diaphragm onthe concave side thereof as distinguished from the convex side.

The novel features that I consider characteristie of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of certain specificembodiments, when read in connection with the accompanying drawing, inwhich:

Fig. 1 is a front view, in elevation, of a soundtranslating deviceconstructed according to my invention. l

Fig. 2 is a cross-sectional view of the same device taken along a linecorresponding to the line II-II in Fig. 1,

Fig. 3 is a front view, in elevation, of a sound'- translating device,of alternative type, also constructed according to my invention,-

Fig. 4 is a cross-sectional view of the device shown in Fig. 3 takenalong a line corresponding to the line IV-IV in that ligure,

Fig. 5 is a fragmentary View, partly in section, of a base plate ofalternative type,

Fig. 6 is a View, partly sectional and partly diagrammatic, of analternativeV form of coilsupport and centering device, and

Fig. '7 is an end view of the centering device shown in Fig. 6.

lThe apparatus illustrated in Figs. l and 2 of the drawing includes aU-shape permanent magnet 1 having an opening 3 in the flat portion,connecting the legs 5 thereof, of sufcient size to accommodate avoice-coil '7 and a central pole piece 9. The central pole piece extendsrearwardly from a base platei 11, of magneticl mateirial, to. which thelegs of the U-shape magnet Vbetween a plurality of diaphragm mountingrings -19 and 21.

The mounting rings provide a supporting frame for the periphery of thediaphragm, which frame is held firmly against or anchored to the innersurface of the base plate 11 by a plu-v rality of bolts 23 or equivalentdevices, whereby the diaphragm lies entirely within the legs of theU-shape magnetic elementI and is protected thereby.

The voice coil 7 is carried by a cup-shape coil form axed to the smallerend of the diaphragm, the said form being centered with respect to theannular air-gap defined by the central pole piece and the opening in theU-shape magnet by a centering device 27, such as a screw or thelike,which projects through the bottom of the coil-form into the end ofthe central pole piece.

' The-'magnetic system, constituted by the bas plate 11, the U-shapeelement 1, and the central pole piece 9 may, alternatively, be energizedby a eld coil 29, as shown in Fig. 4 of the drawing.

It also lies within the scope of my invention to utilize the base plateas a protective grille for the device, as is shown in Figs. 3 and 4 ofthe drawing, wherein elementsA similar to those illustrated in Figs. 1and 2 are similarly desig- V nated.

A -The essential difference between the device illustrated in Figs'. 3and 4 and the modified device shown in Fig. 1, lies in the substitutionof a larger cover plate 31, through which extend a plurality ofperforations 33, for the small baseplate 11. The' perforations may becircular, as shown, or they may be given any ornamental configurationdesirable.

The cover plate, vwhich is also a part of the magnetic circuit, isprovided With a plurality of diametrically disposed ears 35 through eachof which extends a bolt 37 that cooperates with a suspension lug 39 forthe purpose of rmly vclamping the device to the margin of Yan opening ina wall orin an analogous position.

It is also feasible to dispense with the bolts 23 that hold thediaphragm clamping rings 19 and 21 against the rear surface of thebaseplate. In such event it is convenient to increase the diameter ofthe outer ring 19 and to clamp it-betweenashoulder 41 on the U-shapeelement 11v and the base-plate by means of the screws 13 that hold thebase-plate Yand the U-shape element together.

From the foregoing description it will be seen that the magnetic circuitsurrounds the diaphragm and that a portion thereof, such as the polepiece 9, extends entirely through the space bounded by the inner surfaceof the diaphragm, such space, as hereinbefore pointed out, being thatspace bounded by the surfaces of the concave side of the diaphragm. Thisspace is also adapted to receive and to provide for an acoustic loadingmeans, as will hereinafter be described in connection with Fig. 5.

Furthermore, I have found it desirable, where complete protection of thediaphragm is essential and economy is not an importantfactor, to utilizeacup-shaped element entirely enclosing the diaphragm,instead of theU-shape magnet shown. When using the cup-.shape element it is desirableto provide one or more openings 43 therethrough to prevent the entrappedair from del-V soy a beam. The diffusing means may take the form of aseparate conical element (not shown) sur-` rounding the central polepiece and the eld coil (if one is used), the contour of the said elementapproximating the contour of the inner surface' of the cone. The spacingbetween the sound diffusing element and the inner surface of the cone isdifficult to predict accurately inasmuch as the said spacing is, toafgreat extent, dependent upon the diameter of the cone, the maximumamplitudey of movement thereof, the size of the openingsV in the grilleand upon other variable factors.

If it were possible to make the entire base plate of relatively thinsheetmaterial the cost of the device would, to some extent Abe lessened.Too thin material, however, gives rise to undesirable magneticsaturation at the point of attachment of the central pole-piece. I,therefore, propose to increase the thickness of an otherwise relativelythin plate, substantially as shown in Fig. 5,- by the addition of .aprotuberant portion 45.

In addition to improving the magnetic circuit of the device theprotuberant portion may be given such a configuration that it serves asan effective diffuser for high frequency sounds while offering lowimpedance to sounds at low frequencies.

Direct egress for low frequency sounds is provided for by a plurality ofsmall openings 47, extending through the protuberant portion, Whilesounds at high frequencies which do not pass readily through the smallopenings 47, are caused to detour, so to speak, by the inner face of thesaid portion to emerge, together with sounds at lower frequencies, froma plurality of larger openings 49 provided in the thinner part of theplate. The high frequency sounds are thereby prevented from beingdirected from the diaphragm in a beam.

The openings 47 have relatively high acoustic Yinertance with respect tosounds at high frequencies but present relatively low impedance to thepassage of loW frequnecy sounds and their presence does not adverselyinfluence the diaphragm at such frequencies. In effect, therefore, thediffuser is a low-pass acoustic filter.

Acoustic loading material may be inserted in the openings 47 and 49, ifdesirable, as shown at 49h in openings 49 for example.

The leads to the voice-coil in either of the alternative forms of myimproved device may be brought out from the rear thereof in any desiredmanner. For example, it is feasible to connect one of the leads directlyto the centering device 27 and to connect the other to a metallicsoldering lug, or the like, carried upon the bottom of the voice-coilform, from which a single flexible connection may extend to an insulatedbinding post mounted upon the U-shape magnetic element.

I prefer, however, to dispense entirely with the bottom of 'thecoil-form, through whichthe centering device extends, and to utilize,instead,

a plurality of resilient metallic elements 51 and 52 that also serve asintermediate means for connecting the voice coil '7 to the outputterminals 53 of an amplifier or the like, as shown in Fig. 6.

The metallic elements, which may be corrugated to give them therequisite amount of compliance, are disposed at right angles to eachother and are separated by an insulating spacer 55. The ends of each ofthe elements are bent over to embrace the coil-form 25 and they may beaflixed thereto by cement or by other appropriate means, such asriveting.

Each element has a central opening 57 slightly larger in diameter thanan insulating sleeve 59 which extends therethrough, to permit of lateralmovement of the assembly for centering, upon loosening of a clampingbolt 61 threadedly connected to the end of the central pole piece. Thehead of the clamping bolt is insulated from the rearwardly disposedresilient element 51 adjacent thereto by a Washer 63 of appropriatematerial such as micanite or the like.

One terminal of the voice-coil is connected to the metallic element 52,which rests against and is in conductive engagement with the pole piece9, and the other terminal is connected to the metallic element 5l whichis provided with a soldering lug 65.

The leads 53, from the ampliiier (not shown) are connected,respectively, to the pole piece 9, or to any part of the magneticcircuit components, and to the soldering lug, thus obviating thenecessity for flexible connections to the voicecoil.

It will be apparent from the foregoing description of my improvedsound-translating device that it is extremely compact and that it ispeculiarly adapted for use in situations where space is at a premium andwhere protection of the diaphragm against injury is essential. Myimproved sound-translating device is also advantageous in that itradiates sound substantially non-directively by reason of the inclusiontherein oi elements constituting a low-pass acoustic lter and a diffuserfor sounds at high frequencies.

Ihe elimination of flexible leads is also an important phase of myinvention since such leads are very prone to break during use.

Although I have illustrated and described several specific embodimentsof my invention, numerous modifications thereof will be apparent tothose skilled in the art to which it pertains. My invention, therefore,is not to be restricted except insofar as is necessitated by the priorart or bythe spirit of the appended claims.

I claim as my invention:

l. In a sound-translating device, a diaphragm having a surface ofrevolution, a voice-coil form affixed to said diaphragm, an element of amagnetic system extending entirely through the space bounded by saiddiaphragm and supporting means for said voice-coil form carried by saidelement.

2. In a sound translating device, a substantially conical diaphragm, anelement of a magnetic system extending entirely through the spacebounded by the inner surface of said diaphragm, and high frequency soundimpedance means disposed within the space bounded by the inner surfaceof said diaphragm and immediately adjacent to the axis thereof, wherebythe projection of a narrow beam of high frequency sounds issubstantially prevented.

3. In a sound translating device, a substantially conical diaphragm, anelement of a magnetic system extending entirely through the spacebounded by the inner surface of said diaphragm, and Vhigh frequencysound-diverting means disposed within the space bounded by the innersurface of said diaphragm and immediately adn jacent to the axisthereof, whereby the projection of a narrow beam of high frequencysounds is substantially prevented.

4. In a sound-translating device, a substantially conical diaphragm, avoice-coil form carried by the smaller end of said'diaphragm, an elementof a magnetic circuit extending through the space bounded by saiddiaphragm and into said coil form and means exterior of said diaphragmfor centering said coil with respect to said ele ment, said centeringmeans being directly connected with and carried by the end of saidmagnetic circuit element which extends into said voice coil form.

5. In a sound-translating device, a substantially conical diaphragm, avoice-coil form carried by the smaller end of said diaphragm, an elementof a magnetic circuit extending through the space bounded by saiddiaphragm and into said coil form and means exterior of said diaphragmfor centering said coil with respect to said element, said voice-coilform being cup shaped and enclosing the end of said magnetic circuit element extending into it, and said centering means being carried by saidend of the magnetic circuit element and extending through the bottom ofsaid cup shaped coil form to cooperate therewith.

6. In a sound translating device, a substantially conical diaphragm, anelement of a magnetic system extending entirely through the space 1"bounded by the inner surface of said diaphragm, and acoustic filteringmeans disposed within the space bounded by the inner surface of said diaphragm and immediately adjacent to the axis thereof, whereby theprojection of a narrow beam of high frequency sounds is substantiallyprevented.

'7. In a sound translating device, a substantially conical diaphragm, anelement of a magnetic system extending entirely through the space fbounded by the inner surface of said diaphragm, and low pass acousticfiltering means disposed within the space bounded by the inner surfaceof said diaphragm and immediately adjacent to the axis thereof, wherebythe projection of a narrow beam of high frequency sounds issubstantially prevented.

8. In a loudspeaker, a magnet member, a conical diaphragm disposedwithin the boundaries thereof, and a plurally perforated plate ofmagnetically permeable material covering the base oi the diaphragm andbeing in contact with diametrically opposite portions of said magnetmember, the perforations adjacent the center of said plate beingmaterially smaller in diameter than the perforations adjacent theperiphery thereof, whereby, when the loudspeaker is in operation, theprojection of a narrow beam of high frequency sounds is substantiallyprevented.

9. The invention set forth in claim 8 characterized in that acousticloading material is disposed in certain of the larger perforationsremote from the center of the plate.

10. The invention set forth in claim 8 characterized in that the centerof the plate provided with the smaller perforations is materiallythicker than the periphery thereof.

11. In a sound translating device, the combination with a conicaldiaphragm, of a protective casing enclosing said diaphragm andcomprising a base plate adapted to form closure means for a wall openingand a cup shape member secured tothe base plate and enclosing thediaphragm between it and the base plate, said cup shape member having acentral opening, a coil form connected with the diaphragm located insaid opening, a central pole piece secured to the base plate andextending through said opening and within the coil form, and meanssecured to the end of the pole piece adjacent the coil form foradjusting the position of the coil form within the opening, said meansextending exteriorly of the casing, whereby the coil form maybe adjustedwithout dismantling the device. f

l2. In a sound translating device, the combination with a conicaldiaphragm, of a protective casing enclosing said diaphragm andcomprising a base plate adapted to form closure means for a wall openingand a cup shape member secured to the base plate and enclosing thediaphragm between it and the base plate, said cup shape member having acentral opening, a coil form connected with the diaphragm located insaid opening, a central pole piece secured to the base plate andextending through said opening and within the coil form, and meanssecured to the end of the pole piece adjacent the coil form foradjusting the position of the coil form within the opening, said meansextending exteriorly of the casing whereby the coil `form may beadjusted Without dismantling the device, said last named means beingarranged to provide electrical circuit terminals and including twoinsulated, resilient, metallic members secured to the coil form atspaced points, and said base plate having a plurality of openings ofdifferent size, the smaller openings being more adjacent to the centerof the plate, whereby an acoustic filter is provided.

13. In a sound translating device, the combination of a base plateadapted to be mounted in a wall opening and having openings providing agrille, a magnet having its legs secured to the base plate in a positionto lie within said wall opening, said magnet having a central openingspaced from the base plate, a coil form in said opening, a central polepiece extending from andsecured to the base plate, said pole piecehaving one end located Within the coil form and said central opening, afrustro-conical diaphragm flexibly secured along its case end to thebase plate and at its opposite end to one end of the coil form, andmeans extending from said end of the pole piece exteriorly of thecentral opening, whereby the coil form may be adjusted. Y

14. In a sound translating device, the combination of a base plateadapted to be mounted in a wall opening and having openings providing agrille, a cup shape magnet having an edge secured to the base plate in aposition to lie Within said wall opening and adapted to form a closedpro tective cover at the rear of the plate, said magnet having a centralopening spaced from the base plate, a con form in said opening, acentral pole piece extending from and secured to the base plate, saidpole piece having one end located within the coil form and said centralopening, a frustro-conical diaphragm flexibly secured along its base endto the base plate and at its opposite end to one end of the coil form,means extending from said end of the pole piece exteriorly of thecentral opening, wherebylthe coil form may be adjusted, and anelectro-magnetic field coil surrounding the central pole piece andlocated between the inner conical face of the diaphragm and the baseplate, whereby it is adapted to pass a magnetic ilux through the baseplate, the vcup shape magnet and the central pole piece.

15. In a sound translating device, the combination of a base plateadapted to be mounted in a wall opening and having openings providing agrille, a cup shape magnet having an edge secured to the base plate in aposition to lie Within said wall opening and adapted to form a closedprotective cover at the rear of the plate, said magnet having a centralopening spaced from the base plate, a coil form in said opening, acentral pole piece extending from and secured to the base plate, saidpole piece having one end located Within the coil form and said centralopening, a frustro-conical diaphragm flexibly secured along its base endto the base plate and at its opposite end to one end of the coil form,and means extend-v ing from said end of the pole pieceY exteriorly ofthe central opening, whereby thecoil form may be adjusted, certain ofrsaid openings adjacent the center of said base plate being ofrelatively small size for the passage of low frequency sounds, andcertain others of said openings being of a larger size for the passageof low and high frequency sounds, thereby to provide a sound filter, anda Ventilating opening in said cup shape magnet.

16. ln a sound translating device, the combination of a base plateadapted to be mounted in a Wall opening and having openings providing agrille, a magnet having its legs secured to the base plate in a positionto lie within said wall opening, said magnet having a central openingspaced from the base plate, a coil form in said opening, a centrai polepiece extending from and `secured to the oase plate, said pole piecehaving one end located within the coil form and said central opening, afrustro-conical diaphragm flexibly secured along its base end to thebase plate and at its opposite end to one end of the coil form, meansextendingfrom said end of the pole piece exteriorly of the centralopening, whereby the coil form may be adjusted, said means being adaptedtoresiliently connect the opposite end of the coil form with the polepiece and including two resilient metallic elements adjustably securedto the adjacent end of the central pole piece and being further securedto the coil form at spaced points, and means for insulating saidelements whereby they are adapted to provide electrical circuitterminals. i

l'l. An electrical sound translating device including in combination, abase plate of magnetic material, a conical diaphragm mounted on andsupported by said base plate, the base of said diaphragm being adjacentvto said base plate, a magnetic core member mounted on the base plateand extending therefrom through the apex of the conical diaphragm, and aframe of magnetic material surrounding the apex of said conicaldiaphragm and detachably secured to the base plate independently of thediaphragm, whereby said frame may be removed from the base plate Withoutinterfering with the diaphragm.

ABRAHAM SOMER RINGEL.

